I want you to start with the idea that I'm an idiot, but don't those exist to be a fire escape from the basement? Wouldn't filling it in negate that, or at least make it more difficult? Again, idiot that lives in the state with the water line two inches below the ground (Florida), which prevents us from making basements.
If that's not true, maybe you'll get someone that comes here to tell me how wrong I am, and gives you great ideas to do with the 'not fire escape'.